For example, Patent Documents 1 and 2 disclose an impulse type turbine impeller which is used for a spindle system or paint spraying system. This turbine impeller is provided with a plurality of turbine blades which receive gas which is ejected from nozzles. The turbine blades are specially designed in shape so as to improve the efficiency of converting the impact force of the ejected gas to a rotational drive force of the turbine impeller.
Specifically, each of the turbine blades is provided with a rear curved surface which is oriented to the rear in the rotational direction of the turbine impeller and receives the gas and with a front curved surface which is oriented to the front in the rotational direction of the turbine impeller and faces a rear curved surface of the adjoining turbine blade, but it is possible to define the rates of curvature of the two curved surfaces so as to improve the exhaust efficiency of the gas from the turbine impeller. As a result, low flow rate gas is used to realize high speed rotation and high torque.